Continuously variable transmission (CVT) systems are used in vehicles to change transmission ratios between an engine output and a drive train of the vehicle. In a typical CVT system, a primary clutch is coupled to receive a rotational output from an engine and a secondary clutch is coupled to provide a rotational output to the drive train. The primary clutch is coupled to provide rotation to the secondary clutch with an endless loop drive belt. In changing transmission ratios, typically the primary clutch is comprised of first and second conical-faced sheave portions that are configured in a way to move the second conical-faced sheave portion axially in relation to the first conical-faced sheave portion along an axis of rotation. In this system the distance between the sheaves of the primary clutch determines the positioning of the drive belt in relation to the rotational axis and hence the transmission ratio. In particular, the closer the first and second sheave portions are positioned together, the farther the drive belt is pinched on the conical-faces away from the rotational axis of the primary clutch. Likewise, the farther the first and second sheave portions are positioned away from each other, the closer the drive belt is the rotational axis of the primary clutch. When the engine is at idle speeds, the first and second sheaves of the primary clutch are axially positioned at a select distance from each other so at least one of the conical faced sheave portions does not engage a side of the drive belt. In this situation, the limited friction between the drive belt and the primary clutch allows the belt to slip so no rotational force is applied to the secondary sheave and hence no power is provided to the drive train by the engine.
Typically CVT systems as described above do not allow for engine braking. Engine braking is a term used to describe when the engine of a vehicle is used to provide at least some of the braking for the vehicle. An example situation where engine braking is beneficial occurs when a vehicle is going down a steep incline and the operator cuts back on the throttle. In this situation the engine's rotational output will be slower than the rotation of the drive train. In an engine braking scheme, the slow rotation of the engine is used to slow down the rotation of the drive train. However, since the drive belt on a typical CVT system is designed to slip on the primary clutch during idle speeds of the motor, the engine effectively is disconnected from the drive train. This disconnection between the engine and the drive train prevents a typical CVT system from implementing engine braking. In this situation, other traditional braking means must be employed which may or may not be effective in a given situation.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an efficient and effective engine braking mechanism in a CVT system.